1. Field of the Invention
This invention relates to an optical pick-up device adapted for reproducing information signals recorded in a signal recording area of a disc-shaped optical recording medium such as an optical disc or magneto-optical disc, etc., or recording information signals onto such optical recording medium.
In the specification of the invention of this application, the above-mentioned optical recording medium will be referred to as optical disc hereinafter.
2. Description of the Related Art
As representative of optical recording media used in an optical disc recording and/or reproducing apparatus, there are known optical discs having a diameter of 64 mm onto which information signals, e.g., audio signals, etc. of recording time of about 74 minutes can be recorded. As shown in FIGS. 1 and 2, with a view of protecting an optical disc 1 at the time of non-use such as storage, etc. and attaining simplicity of handling, the optical disc 1 is rotatably contained (accommodated) within a cartridge body 5 of a structure in which square upper and lower halves 3 and 4 are formed of molded synthetic resin material, and are connected with their rising peripheral walls being butted to each other. The above-mentioned optical disc recording and/or reproducing apparatus will be referred to as a recording/reproducing apparatus.
On the lower half side 4 of cartridge body 5, there is an opening 6 for admission of a disc turn table of a disc rotary drive mechanism to rotationally drive the optical disc 1 contained in disc cartridge 2 that is loaded into the recording/reproducing apparatus.
In a more practical sense, as shown in FIG. 2, this disc turn table admission opening 6 is formed in such a manner as to expose the central portion of optical disc 1, which includes a metallic plate 7 for magnetic clamping.
Moreover, at upper and lower surfaces of cartridge body 5, i.e., upper and lower halves 3 and 4, there are openings 8, 9 for recording/reproduction of information signals such that at least a portion of the signal recording area of optical disc 1 contained therein is exposed toward the outside.
These information signal recording/reproduction opening portions 8, 9 have a square form and extend from the front end surface side of cartridge body 5 to a position close to the disc table admission opening 6 as shown in FIGS. 1 and 2.
These information signal recording/reproduction opening portions 8, 9 are opened and closed by a shutter 10 which is substantially U-shaped in cross section and is fitted and disposed from the front end surface side of cartridge body 5.
Namely, when this disc cartridge 2 is not used, information signal recording/reproduction opening portions 8, 9 are closed by shutter 10. When this shutter 10 is located at the position where information signal recording/reproduction opening portions 8, 9 are closed, it is locked by a lock member disposed within cartridge body 2, and is held at the closed position.
The disc cartridge 2 constituted in a manner described above is formed so as to have dimensions sufficient to accommodate optical disc I having diameter (R) of 64 mm as indicated by single dotted slanting lines of FIG. 1.
In actual terms, this disc cartridge 2 is formed so that width (W1) in a direction where shutter 10 moves to open and close information signal recording/reproduction opening portions 8, 9 is 68 mm, width (W2) in a direction perpendicular to the direction where shutter 10 moves is 72 mm, and thickness (D) is 5 mm.
Moreover, information signal recording/reproduction opening portions 8, 9 formed at cartridge body 5 are formed so that length (L1) extending in the radial direction of optical disc 1 is 24 mm and width (W3) is 17 mm as shown in FIG. 2. By employing such a compact disc cartridge 2 for storage of recording medium, it is possible to miniaturize the recording/reproducing apparatus itself.
Meanwhile, in recording/reproducing apparatus using an optical disc as recording medium, there is provided an optical pick-up device adapted for converging (focusing) incident laser beams emitted from a light source such as semiconductor laser, etc. into the signal recording area of optical disc 1 to irradiate them thereinto, and detecting return laser beams from the optical disc 1 to thereby record information signals onto optical disc or to reproduce information signals recorded on the optical disc 1.
This optical pick-up device comprises an optical system block comprised of optical parts of a semiconductor laser as a light source for emitting incident laser beams irradiated onto optical disc 1, a photo detector for detecting return laser beams from optical disc 1, and a beam splitter, etc. for carrying out separation of incident laser beams emitted from the semiconductor laser and return laser beams from optical disc 1; and an object lens drive unit provided with an object (objective) lens for focusing incident laser beams emitted from the light source into the signal recording area of optical disc 1 and for allowing incident laser beams to follow recording tracks of the optical disc.
An object lens drive unit constituting an optical pick-up device used in conventional recording/reproducing apparatus comprises, as shown in FIG. 3, base member 11 constituting a magnetic circuit section, bobbin support 12 attached on this base member 11 in a cantilever supporting manner, and bobbin 14 supported on the bobbin support 12 with object lens 13 being attached thereon.
A pair of supporting pins 16, 17 positioned on both sides of base end portion 15 and adapted for supporting fixed portion 24 provided on the base end side of bobbin support 12 are vertically provided on base member 11.
At both sides of the front end sides of base member 11 opposite to the base end side where the supporting pins 16, 17 are vertically provided, a pair of yokes 18, 19 formed in a rising manner (hereinafter simply referred to as rising-formed) so as to take substantially U-shape are provided.
At inside surfaces of one pieces 18a, 19a constituting the yokes 18, 19, magnets 20, 21 are respectively attached.
Bobbin support 12 is comprised of molded body of synthetic resin material and includes fixed portion 24 in which pin through (penetration) holes 22, 23 through which supporting pins 16, 17 are respectively inserted are bored at the base end side thereof.
From one side surface of this fixed portion 24, a pair of parallel supporting arms 25, 26 are extended. Front end sides of the parallel supporting arms 25, 26 are connected by connecting piece 28.
At the connecting portion side to the fixed portion 24 and the connecting portion side to the connecting piece 28 of the pair of parallel supporting arms 25, 26, focusing direction displacement portions 27a, 27b and 29a, 29b which are caused to have a small thickness are respectively formed in parallel and extending in the width direction.
By forming focusing direction displacement portions 27a, 27b and 29a, 29b in a manner as described above, a pair of parallel supporting arms 25, 26 can be caused to undergo displacement in parallel to the axial direction of supporting pins 16, 17 for supporting fixed portion 24.
At the front end surface sides of connecting pieces 28, bobbin attachment portion 32 is provided through thin tracking direction displacement portion 31 formed in,parallel to the axial direction of supporting pins 16, 17 for supporting fixed portion 24.
At bobbin attachment portion 32, tubular formed bobbin 14 is attached. At this bobbin 24, lens attachment portion 33 for attaching object (objective) lens 13 at one side thereof is integrally provided.
Object lens 13 is attached on this lens attachment portion 33 through a lens holder fitted and disposed in a fitting hole formed at lens attachment portion 33. Extending from the other end side of bobbin 14 to the central portion thereof, substantially U-shaped cut portion 34 in which a pair of parallel supporting arms 25, 26 extend are formed.
At the side surface of the inner side of the cut portion 34, fitting recessed portion 35 into which bobbin attachment portion 32 provided at the front end side of bobbin support 12 is fitted is formed. At the opening end side of the cut portion 34, weight 36 for maintaining weight balance with respect to object lens 13 attached on lens attachment portion 33 is attached.
At the both side portions opposite to each other of bobbin 14, coil attachment portions 37, 38 formed in a recess shape are provided.
At the coil attachment portions 37, 38, focusing coils 39, 40 wound in a square tubular form are respectively attached. At the outer side surface sides of these focusing coils 39, 40, respective pairs of tracking coils 41, 42 wound in a flat square form are attached.
Bobbin 14 in which object lens' 13 is attached on bobbin attachment portion 32 through lens holder is supported on bobbin support 12 by fitting bobbin attachment portion 32 provided at the front end sides of a pair of parallel supporting arms 25, 26 into fitting recessed portion 35 formed at the side surface of the inner side of cut portion 34.
Bobbin support 12 on which the bobbin 14 is supported is attached on base member 11 by inserting supporting pins 16, 17 into pin through holes 22, 23 bored at fixed portion 24. Thus, object lens drive unit is constituted.
Magnets 20, 21 attached to one pieces 18a, 19a are respectively caused to be opposed to focusing coils 39, 40 and tracking coils 41, 42 as the result of the fact that the other pieces 18b, 19b of yokes 18, 19 provided at base member 11 are inserted through tubular formed focusing coils 39, 40 which are attached to bobbin 14.
In the object lens drive unit thus constituted, when a drive current corresponding to focus error signal is delivered to focusing coils 39, 40, a driving force in the focusing direction which is the direction in parallel to the optical axis of object lens 13 is produced in cooperation with magnetic flux of magnets 20, 21.
By this driving force, a pair of parallel supporting arms 25, 26 are caused to undergo elastic (resilient) displacement in the focusing direction indicated by arrow F in FIG. 3 with focusing direction displacement portions 27a, 27b and 29a, 29b being the point of displacement.
By this elastic (resilient) displacement, object lens 13 attached on bobbin 14 supported at the front end sides of a pair of parallel supporting arms 25, 26 is displaced in the focusing direction. Thus, focusing with respect to optical disc 1 is carried out.
When a drive current corresponding to tracking error signal is delivered to tracking coils 41, 42, driving force is produced in tracking direction perpendicular to the optical axis of object lens 13 in cooperation with magnetic flux of magnets 20, 21.
By this driving force, bobbin 14 supported at the front end sides of a pair of parallel supporting arms 25, 26 is caused to undergo displacement in tracking direction which is the direction indicated by arrow T in FIG.@ 3 with tracking direction displacement portion 31 being the point of displacement.
As the result of the fact that object lens 13 is caused to undergo displacement in the tracking direction (radial direction of optical disc 1) which is the direction perpendicular to the optical axis of object lens 13 as described above, tracking control conducted so that laser beams follow recording tracks of optical disc 1 is carried out.
An optical block constituting an infinite optical system comprised of optical parts including the above-mentioned object lens 13 shown in FIG. 4 is combined with the object lens drive unit constituted in a manner stated above. Thus, an optical pick-up device is constituted.
This infinite optical system constitutes a first optical path by optical parts (components) of semiconductor laser 44 as a light source for emitting laser beams, grating 45 serving as a diffraction lens for optically separating components of emitted laser beams (into spectral components), beam splitter 46 for optically separating a portion of laser beams (into spectral components), and collimator lens 47 for changing laser beams passed through the beam splitter 46 into laser beams (rays) of parallel light, which are disposed on the same optical axis, and reflection mirror 48 disposed at an angle of 45 degrees relative to the above-mentioned optical axis and adapted to change traveling direction of laser beams by 90 degrees to allow them to be incident to object lens 13.
Further, the infinite optical system constitutes a second optical path by multi-lens 49, and photo detector 30 comprised of photo detecting element to which reflected laser beams passed through the multi-lens 49 are incident, which are disposed oppositely to beam splitter 46 on the optical axis perpendicular to the above-described first optical path.
Accordingly, laser beams irradiated onto the signal recording area of optical disc 1 through object lens 13 are reflected by the optical disc 1, and rays of reflected light are incident to object lens 13. Further, rays of light emitted from the object lens 13 are incident to reflection mirror 48, by which traveling direction is changed by 90 degrees. The rays of reflected light thus obtained are then incident to beam splitter 46 through collimator lens 47.
At the beam splitter 46, traveling directions of the reflected laser beams are changed by substantially 90 degrees and are separated into@spectral components toward side directions. The spectral components thus obtained are then incident to multi-lens 49. In order to improve sensitivity and accuracy of photo detector 30, this multi-lens 49 shapes reflected laser beams to allow those shaped laser beams to be incident to photo detector 30. This multi-lens 49 is supported by multi-lens holder 49A adjustably movable along the optical axis of the second optical path. By implementing adjustably movable operation to the multi-lens holder 49A, reflected laser beams are caused to be incident to photo detector 30 in an optimum state.
Meanwhile, in the object lens drive unit conventionally used, as described above, fixed portion 24 provided at the base end side of bobbin support 12 is supported by base member 11, and bobbin 14 on which object lens 13 is attached is supported through bobbin attachment portion 32 provided at the front end sides of a pair of parallel supporting arms 25, 26 extending from the fixed portion 24.
Further, the magnetic circuit section composed of yokes 18, 19 and magnets 20, 21, which produces a driving force for driving object lens 13 attached on bobbin 14 to allow it to undergo displacement in a direction in parallel to the optical axis of object lens 13 and in a direction perpendicular to the optical axis along with focusing coils 30, 40 and tracking coils 41, 42 attached at the bobbin 14, is of a structure in which it is disposed between fixed portion 24 to base member 11 and object lens 13.
For this reason, a pair of parallel supporting arms 25, 26 for supporting bobbin 14 are elongated, and the length from fixed portion 24 to the front end of bobbin 14 also becomes great. As a result, the object lens drive unit itself also becomes large-sized.
Accordingly, when such object lens drive unit is applied to recording/reproducing unit using for storage of recording medium, disc cartridge 2 within which the above-described optical disc having diameter of 64 mm is contained, only a portion of bobbin 14 including object lens 13 is faced to information signal recording/reproduction opening portions 8, 9 provided at cartridge body 5, and the remaining portions would be disposed in the state extended to the lower surface side of cartridge body 5.
For this reason, object lens drive unit is required to be disposed at a position remote from the lower surface of disc cartridge 2 mounted in recording/reproducing apparatus in order that when object lens 13 is caused to undergo displacement in optical axis direction, bobbin 14 and/or bobbin support 12 are not in contact with cartridge body 5 of the peripheral edge, etc. of information signal recording/reproduction opening portion 9.
When object lens drive unit is disposed at a position remote from disc cartridge 2 in this way, focal distance (length) of object lens 13 which places a focal point of light flux in the signal recording area of optical disc 1 also becomes large.
As a result, object lens 18 further becomes greater, leading to further enlargement of object lens drive unit provided with such object lens 13. Accordingly, it extremely becomes difficult to realize miniaturization of recording/reproducing apparatus using such object lens drive unit.
In view of,this, there has been already proposed an object lens drive unit in which a differential distance, which is the distance from the end surface of object lens 13 up to the signal recording area of optical disc 1, is reduced to permit employment of compact object lens 13 having small focal distance, thereby making it possible to allow such unit to be compact.
This object lens drive unit has a configuration as shown in FIG. 6 such that lens supporting piece 43 is projected, i.e. , provided in a projected manner from the upper surface of one end side of bobbin 14, lens attachment portion 33 is provided on the lens supporting piece 43, and object lens 13 is attached through the lens attachment portion 33. By employing such configuration, object lens 13 is caused to be faced into information signal recording/reproduction opening portions 8, 9 of disc cartridge 2. For this reason, the object lens 13 can be close to optical disc 1.
Accordingly, in this object lens drive unit, the differential distance between object lens 13 and optical disc 1 can be reduced. In this case, compact object lens 13 is employed, thereby making it possible to further miniaturize the entirety of the unit.
However, even if object lens 13 is caused to be compact to realize miniaturized (compact) object lens drive unit in this way, since this unit is of a structure in which portions except for object lens. 13 are disposed in the state extended to the lower surface side of cartridge body 5, recording/reproducing apparatus provided with such object lens drive unit cannot be compact as a whole.
Further, in the object lens drive unit adapted so that object lens 13 is attached through lens supporting piece 43, deformation of lens supporting piece 43 or parallel supporting arms 25, 26 becomes conspicuous by aged deterioration. For this reason, the optical axis of object lens 13 was inclined, resulting in the problem that the optical axis cannot be maintained vertically to optical disc 1 with high accuracy.
Further, in the above-described object lens drive unit, since only the object lens 13 is projected from bobbin 14 so as to allow it to be close to optical disc 1, object lens 13 would, be disposed at a position spaced from the magnetic circuit section which produces the driving force. Thus, it becomes difficult to allow the object lens 13 to undergo displacement with good response with respect to driving force corresponding to focus error signal and tracking error signal.
As a result, the recording/reproducing apparatus became unable to precisely carry out focus control and tracking control of object lens 13, resulting in the problem that there is a possibility that recording and/or reproduction of information signals cannot be carried out with good recording/reproducing characteristics.
Furthermore, in the optical pick-up device in which optical block constituting the infinite optical system is combined with the above-described object lens drive unit, a large-sized beam splitter 46 is required because of large beam diameter. For this reason, the entirety of the device also becomes large-sized. In this case, since the optical path is also long, slightly large-sized multi-lens holder 49A can be used. Thus, multi-lens 49 can be firmly held. However, there was the problem that the entirety of the device is further large-sized.
Accordingly, this invention has been proposed with a view to providing an optical pick-up device in which optical parts including object lens caused to be compact are reasonably arranged, thereby permitting the entirety of the device to be further compact.
Further, this invention has been proposed with a view to providing an optical pick-up device in which adjustment operation of optical parts is facilitated and durability is improved against aged deterioration.